Whenever you have a lidded form, whether it is hand built or thrown, you need to join the lid and jar together as soon as they are dry enough to retain their shape under the weight. This will help ensure that the lid and jar will continue to match one another. (Warping while drying or in the kiln can make a lid unable to fit on its jar, otherwise.)
While the clay is at all damp, you cannot place the lid directly on it or the clay may weld itself to the jar's clay. Therefore, tear pieces of paper towel and lay across the area where lid and jar meet. You can see parts of the paper toweling sticking out in our example photo of this jar with its untrimmed lid.